The three women who spoke publicly on Monday called for Congress to investigate the president.
Sanders, Merkley and Booker ask Trump, who has been dogged by allegations of sexual misconduct, to step down.
Nikki Haley's comments are a departure from the White House position.
Shelby encouraged fellow Alabama voters to do as he did on his absentee ballot: to write in the name of another Republican.
The president got a private tour of the museum and made remarks at a separate event after protests arose over his plans to attend the opening.
Pulitzer Prize-winning reporter Sari Horwitz guides us through Trump's lawyers' comments on the president’s immunity when it comes to obstruction of justice. Plus, legal experts weigh in on differing legal perspectives and how presidential pardoning may play a role in obstruction.
Democrats say that the holdouts are evidence the legislation is unpopular.
"I do know that I spent 12 days on the road with him in Asia, and despite the fact that he's a little bit older than me, he had twice the energy that I do,” White House press secretary Sarah Huckabee Sanders said.
It was Trump's most direct show of support for Roy Moore, with the Senate race a dead heat.
Trump tried to equate Flynn's actions with those of Hillary Clinton, although she has not been charged with lying to the FBI.